This application claims the priority of 198 48 448.8, filed Oct. 21, 1998, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a brake pressure control device of a brake system of a road vehicle with an automatic control of a main clutch and/or of a transmission for the purpose of maintaining a driving condition for the duration of traffic-caused stoppage phases by controlling brake pressure into at least one wheel brake of the road vehicle.
DE 196 11 360 C2 discloses, a device for the automatic operation of a hydraulic brake system of a road vehicle to maintain a vehicle stoppage for the duration of traffic-caused stoppage phases by coupling brake pressure from a brake pressure source, which can be activated without the driver's cooperation, into at least one wheel brake of the vehicle. This device operates with a brake pressure control device which, from a processing of sensor output signals of a sensor arrangement taking place according to plausibility criteria while the engine is running and after stoppage of the vehicle achieved after a braking operation, provides an automatic continuation of the stoppage braking. After a delay period of a defined duration has elapsed from the stoppage of the vehicle, a brake pressure, which is sufficient for a secure stoppage of the vehicle, is coupled into the wheel brake(s) utilized for the stoppage braking. When the driving operation is resumed, which can be detected from a redundant combination of sensor output signals, such as the output signal of an accelerator pedal position generator and a throttle valve position sensor or of a rotational engine speed sensor, the wheel brake(s) previously utilized for the stoppage braking is (are) released.
This known brake pressure control device endeavors to carry out maneuvering operations in a simple and secure manner irrespective of a triggering of stoppage brake operation phases which meet the demand. For this purpose, the automatic stoppage braking operation will be activated only when, within the delay period, the driver starts an operating activity which can be recognized as the driver's wish to activate the automatic stoppage braking and can be detected by the sensor arrangement. The termination of the automatic stoppage braking operation occurs only if, in addition to the sensor output signals of the sensor arrangement which demonstrate the driver's wish to resume the driving operation, sensor output signals are also present which, again on the basis of plausibility criteria, indicate the meeting of safety-relevant secondary conditions.
Thus, in the known control device, the time period is triggered by reaching the stoppage of the vehicle during a stoppage braking. The brake pedal is completely released after the triggering of the stoppage braking, and the continuation of the stoppage braking, when the accelerator pedal is operated for resuming the driving operation, is terminated only if the engine hood and the vehicle doors are closed and the driver's seat is occupied.
The goal of the known brake pressure control device of representing the function of a mechanical hill holder (free wheeling)--specifically automatic prevention of rolling on a hill against the intended driving direction--by way of a brake intervention, cannot be achieved in every operating condition or can be achieved only with high technical expenditures. In practice, problems with the operating comfort may also occur depending on the construction. For example, depending on the surrounding conditions, the vehicle will roll backwards in an undesirable manner because the existing brake pressure is not sufficient. Moreover, because the brake is operated in an undesirable manner in certain operating conditions (so that, for example, the maneuvering on the hill is more difficult) or, during active braking, noise problems occur while standing as the result of the pump of the brake system.